Other names tossed out Monday include Kevin Knobloch, now the chief of staff to Energy Secretary Ernest Moniz but previously the head of the Union of Concerned Scientists; Gary Guzy, the deputy director of the Council on Environmental Quality and a Clinton-era EPA general counsel; and Natural Resources Defense Council President Frances Beinecke.

The administration never fully replaced Browner and ultimately dissolved her old climate and energy office under the Domestic Policy Council’s umbrella. “I think the question is do they try to fill Heather’s position or Carol’s position,” said one Democratic source close to the administration.

One observer questioned why the White House didn’t find a way to get Zichal to stay. Earlier this year, Zichal had been the subject of speculation that she could be in line for a new position in Obama’s administration, perhaps as head of the White House Council on Environmental Quality.

“I am not sure who is in charge of retention programs at the White House but I would have never let Heather leave the complex,” said Brian Wolff, a longtime Democratic political operative now working as the senior vice president of the Edison Electric Institute, the leading trade group for the electric utility industry.

“She is far too valuable of a skilled communicator and negotiator,” he said. “She has been absolutely dogged in her pursuit of gaining consensus with external stakeholders and delivering on a clean energy agenda for this administration.”

The Washington Post said Monday that Obama “personally appealed to Zichal to stay,” and that she had turned down an opportunity to replace CEQ Chairwoman Nancy Sutley. The White House refused to confirm that report Monday afternoon.

Former Vice President Al Gore made what appeared to be a veiled reference to Zichal in June while lamenting that Obama had yet to give climate change a high enough profile in his administration.

“He does not yet have a team in the White House to help him implement solutions to the climate crisis. He hasn’t staffed up for it,” Gore said at the time, adding that “he’s got one person who hasn’t been given that much authority.”

Zichal was certainly much less of a household name than Browner, a former Gore protege who had previously served eight years as former President Bill Clinton’s EPA administrator — and whose “czar” role had made her a big lightning rod for Republicans. Still, one former White House official told POLITICO that Zichal was the most effective person they worked with on energy and environmental issues at the White House, and that her close relationship with the president will be make replacing her difficult.